(a) Field of the Invention
The present invention relates to an ion trap mass spectrometer, and more particularly, to an ion trap mass spectrometer capable of improving mass resolution and detection sensitivity by detecting only ions sequentially released from an ion trap and excluding secondary ions generated out of the ion trap to measure a mass spectrum in the procedure of detection of the ions.
(b) Description of the Related Art
In general, an ion trap mass spectrometer is composed of a donut-shaped ring electrode and two end cap electrodes covering upper and lower portions of the ring electrode.
When an AC voltage is applied between the ring electrode and the two end cap electrodes covering the upper and lower portions of the ring electrode, a quadrupole is formed in the center inside since the two end cap electrodes are connected to each other at the same potential.
As for the simple principle of the ion trap mass spectrometer, a gas sample molecule is ionized by an electron beam, and then the ions are trapped in the thus formed quadrupole. When the AC voltage is increased to change the ion storage conditions, the lighter ions are first released in sequence, and the ion detector measures the released ions, thereby obtaining a mass spectrum showing components and a compositional ratio of the gas sample.
In order to allow the ions released from the ion trap to reach the ion detector, the ions are accelerated at a voltage of about 2000 V to impact on a surface of the ion detector. Here, electrons generated are amplified and then recorded as a current signal.
The accelerated ions impact with other molecules present on a path on which they reach the ion detector to form secondary ions, and secondary electrons are again reversely accelerated to cause another ionization. These procedures are repeated and thus an ion congestion phenomenon occurs.
Since the secondary ions are not ions released from the ion trap but are random ions generated on the path, they cause a difficulty in analyzing the contents of gas components, which are targeted by the mass spectrometer.
In order to remove the secondary ion noise signal, the ion congestion phenomenon is reduced by forming a middle electrode for ion warping between an outlet of the ion trap and the ion detector to thereby allow the secondary ions to deviate from the path, or the background ion noise signal is reduced by forming an ion lens in the middle and applying a pulse type of voltage thereto. However, these methods are not significantly useful.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.